This invention relates to a process for the production of sulfur dioxide from an ammoniacal scrubbing solution obtained in a desulfuration process of coke-oven gas or other H.sub.2 S-containing gases produced from the dry distillation of fossil fuels.
In the desulfuration of coke-oven gas using ammonia, relatively dilute scrubbing solutions are produced which rarely contain more than 20% by weight of combustible components and otherwise consist of water. These solutions contain ammonium thiocyanate, ammonium thiosulfate, sulfur, and free ammonia. The elimination of these solutions represents a considerable problem. They can be burned only with a high expenditure in fuel and yield a combustion gas containing only about 1-2% by volume of SO.sub.2 and thus are only of minor value for further processing, for example to produce sulfuric acid. On the other hand, the emission of this mixture into the atmosphere is likewise not feasible.
It is possible, by the combustion of such a solution with sulfur or hydrogen sulfide as the fuel, to obtain a gas having a higher SO.sub.2 -content (e.g., 6% by volume), suitable for sulfuric acid production. However, in this case, much more sulfuric acid must be produced than that corresponding to the sulfur content of the scrubbing solution. In general, it is undesirable to solve the problem of disposing of the scrubbing solution by such high sulfuric acid production.
Therefore, the procedure employed heretofore was limited to liberating the ammonia from these scrubbing solutions by addition of milk of lime and recovering the ammonia by distillation. In this method residues are produced whose elimination likewise presents a problem.
It is an object of this invention to provide a process for working up the scrubbing solution produced in a process of desulfuration of coke-oven gas which employs ammonia to obtain sulfuric acid in a manner harmless to the environment and in a quantity which corresponds substantially to the sulfur content of the scrubbing solution. It is a further object to provide a method for processing such scrubbing solutions with minimum fuel consumption, in spite of the low sulfur content of the solution, which generally is about 5-10% by weight. Other objects and advantages of this invention will become apparent to those skilled in the art upon further study of the specification and appended claims.